1. Field of the Invention
The present invention relates to a beam output control method for controlling the output from an exposure beam source used for exposing a substrate such as a wafer or the like, in a lithography process for producing, for example, semiconductor devices, liquid crystal display devices, image pickup devices (CCD or the like) or thin-film magnetic heads, a beam output apparatus and an exposure system, and a device manufacturing method using the exposure system. More particularly, the present invention relates to a beam output control method, a beam output apparatus and an exposure system, and a device manufacturing method using the exposure system, suitable for use in an exposure apparatus using a pulse beam as the exposure beam.
2. Description of the Related Art
Recently, for example, in the production of semiconductor devices, there is a prominent tendency to miniaturization of circuits formed on a substrate such as a wafer or the like, in view of demands for reduction in power consumption and production cost.
Semiconductor devices are produced by repeating a step for projecting an image of a mask or a reticle having a circuit pattern formed thereon onto a wafer on which a photosensitive material is applied, to thereby expose the wafer, and a step for developing the wafer.
It is important to control the exposure quantity of the exposure beam in order to form a desired circuit pattern on the wafer. This becomes more important, as the pattern formed on the wafer is made finer.
In a conventional projection exposure apparatus, a part of the exposure beam is branched, and the branched beam is detected by an integrator sensor comprising a photoelectric transducer. Then, during exposure of the wafer (or a glass plate, etc.) on which a photosensitive material is applied, an accumulated exposure quantity on the wafer is detected indirectly via the integrator sensor.
Moreover, as a control for the exposure quantity with a projection exposure apparatus of a static exposure type called as a xe2x80x9cstepperxe2x80x9d, even if either of a continuous light source such as an extra-high pressure mercury lamp, or a pulse laser source such as an excimer laser is used as the exposure source, cut-off control is performed wherein exposure is stopped basically by confirming that the accumulated exposure quantity detected by the integrator sensor has reached a target value.
When the pulse laser source is used as the exposure light source, since it has a dispersion in the energy value for each light pulse, a desired reproducibility of the exposure quantity control precision is obtained by exposing with a plurality of light pulses of at least a fixed number (hereinafter referred to as xe2x80x9cminimum number of exposure pulsesxe2x80x9d).
In this case, for example, at the time of exposing a wafer on which a high sensitivity resist is applied, since the target accumulated exposure quantity is small, if the laser beam from the pulse laser source is used directly, the wafer cannot be exposed with a number of pulses larger than the minimum number of exposure pulses.
As described above, in the case where the target accumulated exposure quantity is small, it becomes necessary, for example, to decrease the output from the laser source itself, or to dim out the light pulses by using a dimming member (attenuator) installed in an optical path of the laser beam in order to expose the wafer with a number of pulses larger than the minimum number of exposure pulses.
Moreover, in a projection exposure apparatus of a scanning exposure type such as a step and scan type, control of the exposure quantity with regard to only one point on the wafer cannot be applied. Therefore, the above described cut-off control cannot be employed.
As a first method for the exposure quantity control in the scanning exposure apparatus, there is used a method of performing the exposure quantity control by simply multiplying the quantity of light of each pulsed radiation (open exposure quantity control method).
Moreover, as a second method for the exposure quantity control in the scanning exposure apparatus, there is also used a method as disclosed in Japanese Unexamined Patent Application, First Publication No. Hei 6-252022. In this method, the accumulated exposure quantity supplied while each point on the wafer passes through an exposure area (illumination field) in a slit form, is measured on a real time basis for each emission of the light pulse, and based on the accumulated exposure quantity, the target energy of the next light pulse is sequentially calculated to thereby control the energy of the next light pulse (each pulse exposure quantity control method).
According to the former first control method, it is necessary to perform fine adjustment of the pulse energy, so that the following relationship is established to obtain the linearity of the desired exposure quantity control, that is, so that the number of exposure pulses becomes an integer:
(target exposure quantity)=(number of pulses)xc3x97(average energy of one pulse)
Here, the average energy of one pulse is a value measured by the integrator sensor just before the exposure. To use this control method, it is necessary to perform fine adjustment of the pulse energy. For that purpose, there is proposed a method for performing fine adjustment of the output from the pulse laser source itself.
Moreover, with this first control method, the dispersion of the accumulated exposure quantity in a shot is suppressed to a desired value or less, by performing fine adjustment of the energy quantity of one pulse before the exposure operation, and balancing the exposure itself by means of exposure using a plurality of pulses. With such an open exposure quantity control method, the effect of decreasing the dispersion in the accumulated exposure quantity is statistically 1/N1/2 (where N is the number of exposure pulses per one point). That is to say, if it is assumed that the dispersion amount in each pulse energy between pulsed radiations is xcex4p, and the average value is p, when the pulse energy is controlled so that the dispersion in energies between pulsed radiations (statistical dispersion) becomes small, the dispersion in the exposure quantity after the N pulse multiplication can be expressed to be (xcex4p/p)/N1/2.
On the contrary, in the latter second control method (each pulse exposure quantity control method), the dispersion in the accumulated exposure quantity can be made smaller than 1/N1/2, by performing fine adjustment of the pulse energy for each pulse emission.
Moreover, it has been found that high precision close to (xcex4p/p)/N can be obtained as the dispersion in the accumulated exposure quantity after the N pulse exposure, by performing feedback control on a real time basis so that, for example, the multiplied pulse energy for each consecutive certain unit time becomes constant.
According to the projection exposure apparatus of the conventional scanning exposure type as described above, there is also used a method wherein when the energy of the pulse laser beam is finely adjusted for a plurality of pulses, or for each pulse, the output from the pulse laser source itself is finely adjusted. In this case, with the conventional control method, an energy monitor comprising a photoelectric transducer is arranged in the output section of the pulse laser source, separate to the integrator sensor arranged in the illumination system, and the output from the pulse laser source is set to be a variable target value by feeding back the output from the energy monitor. Then, as an example, correlation between the output from the integrator sensor and the output from the energy monitor is actually measured and stored, and the target exposure quantity set up based on the output from the integrator sensor is converted into the target output from the energy monitor just before exposure. During exposure, the thus converted target output is supplied to the pulse laser source, and the pulse laser source is controlled so that the output from the energy monitor becomes the target output of the pulse laser source.
As described above, in order to improve the output precision of the pulse laser source, the energy monitor has heretofore been provided in the pulse laser source itself and the output has been subjected to fine adjustment, to thereby obtain high energy precision on the laser manufacturer""s side. As indices representing the precision of the exposure beam output from the pulse laser source, there are standard deviation and moving average. Standard deviation stands for a deviation in the output value of each pulse with respect to a standard value, and moving average stands for an average value of the output value with respect to a predetermined number of pulses.
Conventionally, as the light source used at the time of exposure, or at the time of measurement of a position of a mask (reticle) performed at the time of exposure and before the exposure, or at the time of measurement of a relative position of a mask and a wafer, or at the time of measurement of a focal position of a projection optical system, a laser apparatus having a predetermined specification prepared by a laser manufacturer is installed in the exposure apparatus, and this laser apparatus is used at the time of exposure and at the time of measurement.
As the light source used at the time of performing an exposure with the projection exposure apparatus of the scanning exposure type such as the step and scan method, however, it is preferred that the moving average at the time of outputting a predetermined number of pulses be uniform. On the other hand, with an exposure apparatus of a batch projection type such as a stepper, if the accumulated exposure quantity is different for each shot, semiconductor devices having nonuniform properties are formed on one wafer. Therefore, it is preferred that the dispersion in the energy for each pulse be as small as possible.
Moreover, even in the case where as disclosed in Japanese Unexamined Patent Application, First Publication, No. Hei 10-209031, imaging characteristics of a projection optical system are measured by emitting light from the pulse laser source, while moving a stage for mounting a wafer, it is preferable from the point of measurement precision, that the energy dispersion (standard deviation) for each pulse be small, so that disturbances in the detected light quantity becomes small.
As described above, the output precision of the pulse laser source has heretofore been determined by laser manufacturers. Laser manufacturers improve the output precision so as to improve the uniformity of the moving average, and to adapt the dispersion in the output for each pulse to respective applications. However, the moving average need only have a constant average value in the results for the output predetermined number of pulses, even if the output of each pulse is different. If it is attempted to improve the precision of the moving average, a problem arises in that the energy for each pulse varies. Conventionally, therefore, both the exposure and position measurement are performed using a pulse laser source supplied from laser manufacturers, causing a problem in that the operation of the pulse laser source cannot be switched so as to be adapted to the operation of exposure or position measurement. As described above, there is recently a noticeable trend towards producing semiconductor devices or the like in a minute size. For example, when printed wiring is formed, production of wiring having a fine constant line width, that is, wiring in which the line width does not vary is required. For that purpose, it is necessary to control the output from the laser source so as to be appropriate for each operation, at the time of exposure or at the time of measurement.
In view of the above situation, it is an object of the present invention to provide a beam output control method which can control the operation of a pulse laser source by switching the operation in accordance with the operation of the exposure apparatus provided with the pulse laser source, a beam output apparatus and an exposure system, and a device manufacturing method using the exposure system.
To achieve the above objects, the beam output control method of the present invention is a beam output control method in which an output from a pulse energy source that emits pulses of exposure beam used in an exposure apparatus is controlled, and the method comprises controlling an output from the pulse energy source in accordance with an operation of the exposure apparatus.
According to the beam output control method of the present invention, since the operation of the pulse energy source is switched in accordance with the operation of the exposure apparatus, the pulse energy source can sufficiently exhibit the inherent performance thereof. As a result, exposure beams having appropriate properties can be obtained in accordance with the operation of the exposure apparatus. Therefore, the invention is ideal for producing fine semiconductor devices and for improving precision in position measurement.
Specifically, with the beam output control method of the present invention, control is performed by changing a control mode for controlling the output from the pulse energy source, in accordance with the operation of the exposure apparatus. Moreover, the operation of the exposure apparatus includes an operation for irradiating an exposure beam from the pulse energy source onto a mask to expose a substrate via the mask, and an operation for measurement using the exposure beam from the pulse energy source.
The control mode includes at least two of:
a first mode in which the output from the pulse energy source is controlled based on a detection result of an energy sensor provided within the pulse energy source;
a second mode in which the output from the pulse energy source is controlled based on a detection result of an energy sensor provided in the exposure apparatus;
a third mode in which the output from the pulse energy source is controlled so that dispersions in the energy for each pulse of the exposure beam emitted from the pulse energy source are suppressed; and
a fourth mode in which the output from the pulse energy source is controlled so that dispersions in the integrated energy of a predetermined number of pulses of the exposure beam emitted from the pulse energy source are suppressed.
More specifically, the third mode includes a mode in which the output from the pulse energy source is controlled so that a standard deviation of the energy of the exposure beam from the pulse energy source becomes small.
Moreover, the fourth mode includes a mode in which the output from the pulse energy source is controlled so that dispersions in a moving average of the predetermined number of pulses sequentially emitted from the pulse energy source becomes small.
Moreover, when exposure of the substrate is performed by the exposure apparatus with the substrate being substantially stationary, the third mode is preferably used, and when exposure of the substrate is performed while the substrate is being moved, the fourth mode is preferably used. Furthermore, when the substrate is exposed with the substrate being substantially stationary, or when the substrate is exposed while the substrate is moved, the second mode is preferably used jointly with this.
It is also preferred that when a substrate having a relatively large proper exposure quantity is exposed by the exposure apparatus, the third mode is used, and when a substrate having a relatively small proper exposure quantity is exposed by the exposure apparatus, the fourth mode is used.
Moreover, when an operation is performed by the exposure apparatus without using the exposure beam, the first mode is preferably used.
Furthermore, the beam output apparatus of the present invention is a beam output apparatus that emits exposure beam used in an exposure apparatus. This apparatus comprises:
a pulse energy source that emits pulses of the exposure beam; and
a control system, functionally connected to the pulse energy source, that controls an output from the pulse energy source in accordance with an operation of the exposure apparatus.
According to the beam output apparatus of the present invention, as with the above-described beam output control method, since the operation of the pulse energy source is switched in accordance with the operation of the exposure apparatus, the pulse energy source can sufficiently exhibit the inherent performance thereof. As a result, exposure beams having appropriate properties can be obtained in accordance with the operation of the exposure apparatus. Therefore, the invention is ideal for producing fine semiconductor devices and for improving precision in position measurement.
Specifically, in the beam output apparatus of the present invention, the control system changes a control mode in which the output from the pulse energy source is controlled, in accordance with the operation of the exposure apparatus.
Moreover, the control mode includes at least two of:
a first mode in which the output from the pulse energy source is controlled based on a detection result of an energy sensor provided within the pulse energy source;
a second mode in which the output from the pulse energy source is controlled based on a detection result of an energy sensor provided in the exposure apparatus;
a third mode in which the output from the pulse energy source is controlled so that dispersions in the energy for each pulse of the exposure beam emitted from the pulse energy source are suppressed; and
a fourth mode in which the output from the pulse energy source is controlled so that dispersions in the integrated energy of a predetermined number of pulses of the exposure beam emitted from the pulse energy source are suppressed.
Furthermore, the exposure system of the present invention comprises:
a pulse energy source that emits pulses of exposure beam;
an exposure apparatus that exposes a substrate by using the exposure beam from the pulse energy source; and
a control system that controls an output from the pulse energy source, in accordance with an operation of the exposure apparatus.
According to the exposure system of the present invention, as well as the case with the above-described beam output control method and the beam output apparatus, since the operation of the pulse energy source is switched in accordance with the operation of the exposure apparatus, exposure beams having appropriate properties can be obtained in accordance with the operation of the exposure apparatus. Therefore, the invention is ideal for producing fine semiconductor devices and for improving precision in position measurement.
Specifically, with the exposure apparatus of the present invention, the control system switches the control mode in which the output from the pulse energy source is controlled, in accordance with the operation of the exposure apparatus.
The control mode includes at least two of:
a first mode in which the output from the pulse energy source is controlled based on a detection result of an energy sensor provided within the pulse energy source;
a second mode in which the output from the pulse energy source is controlled based on a detection result of an energy sensor provided in the exposure apparatus;
a third mode in which the output from the pulse energy source is controlled so that dispersions in the energy for each pulse of the exposure beam emitted from the pulse energy source are suppressed; and
a fourth mode in which the output from the pulse energy source is controlled so that dispersions in the integrated energy of a predetermined number of pulses of the exposure beam emitted from the pulse energy source are suppressed.
Moreover, the device manufacturing method of the present invention is characterized by producing a device, using the above described exposure system.
According to the device manufacturing method of the present invention, as well as the case with the above-described beam output control method and the beam output apparatus, since the operation of the pulse energy source is switched in accordance with the operation of the exposure apparatus, exposure beams having appropriate properties can be obtained in accordance with the operation of the exposure apparatus. Therefore, the invention is ideal for producing fine semiconductor devices and for improving precision in position measurement, and devices having high performance characteristics can be produced.